Ever-increasing performance and functionality of circuits, particularly integrated circuits (IC) generally implemented on a semiconductor substrate, like a silicon chip, is a virtual requirement in modern computing and consumer electronics environments. As ubiquitous devices such as mobile phones, personal digital assistants (PDA), personal computers (PC), personal media players, and the like, take an ever-expanding role in the daily lives of people, the market for these devices demands ever-higher levels of performance and functionality at lower costs. To fulfill this market demand, the designers and manufacturers of IC's, such as microprocessors, microcontrollers, and other digital chips such as DMA (Direct Memory Access), memory controllers, and the like, are faced with the optimization and balance of several different and often conflicting requirements. Among the significant competing requirements for the design and manufacture of IC's are cost, performance, exposure of functionality, reduction in size, reduction in power consumption, and reduction or adequate dissipation of heat.
Performance is often measured in terms of some sort of number of operations per unit time, such as MFLOPS (Millions of Floating point Operations Per Second) for math coprocessors, MIPS (Millions of Instructions Per Second) for general purpose processors, etc. At hardware level, higher performance may be achieved in one or a combination of several techniques. These techniques include using higher clock frequency, and thus higher transistor switching rates, wider communication buses (e.g., data bus, control bus, etc.), and one or more memory caches. Additionally, types of components used may also increase performance. For example, GaAs (Gallium Arsenide) transistors may provide better performance at high frequencies than silicon-based CMOS (Complementary Metal Oxide Semiconductor) transistors. Wider communication buses translate to larger chip areas and thus increased size and power consumption. Addition of cache memory, likewise, increases the size and cost of the IC chips. Higher performance types of components, such as some types of transistors, may also increase cost of manufacturing and/or power consumption and heat.
With added performance and functionality to an IC chip comes the burden of providing a signal interface for using such added performance and functionality. For example, a wider data bus requires a greater number of pins in the IC package to expose the data bus to other hardware, such as external memory, external system bus, and other IC chips on an electronic board. The IC chips are generally contained in plastic or ceramic packages with the signals from the IC bonded to pins on the package. The IC chip itself is hidden from sight and is accessible only through the package. Thus, the size of the package is what ultimately counts in terms of size because it is the package that is used in devices or boards, not the IC itself. As such, even if the IC is miniaturized to a desired level, if many signals need to be exposed, the effective size of the package cannot be reduced beyond what is required to expose all signals. For example, if an IC has 128 signals, then the minimum size of the package must accommodate the exposure of 128 pins bonded to each IC signal, respectively, regardless of the size of the IC itself. Several paradigms have been adopted and/or standardized by most IC manufacturers for reducing or better managing the number of interface signals/pins. Some paradigms expose bidirectional signal interfaces to/from a chip while others expose input- or output-only connectivity. However, the common shortcoming in all of the current state-of-the-art signal interface implementations is that each signal requires its own dedicated physical electrical conductor to transmit information.
Therefore, there is a need to reduce the number of pins on an IC package to reduce the effective size of an IC while improving or at least not worsening other requirements, such as functionality, performance, power consumption, cost, and heat generation.